Maneuvering system for earth orbiting satellites with electric thrusters

ABSTRACT

Systems and methods are described herein for mounting a thruster onto a vehicle. A thruster mounting structure may comprise a first, second, and third rotational joint, a boom, and thruster pallet, and a thruster attached to the thruster pallet. The first rotational joint may be attached to the vehicle and configured to rotate in a first axis. The first rotational joint may be connected to the boom and configured to pivot the boom about the first axis. The boom may be connected to the second rotational joint, which is connected to the third rotational joint and configured to rotate the third rotational joint in the first axis. The third rotational joint may be connected to the thruster pallet and configured to pivot the thruster pallet in a second axis that is perpendicular to the first axis.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/858,240, filed Sep. 18, 2015, issuing as U.S. Pat. No.10,046,867 on Aug. 14, 2018, which is incorporated herein by referencein its entirety.

BACKGROUND

Satellites and other spacecraft typically utilize chemical rocketpropulsion systems to propel themselves into orbit and to performmission operations. Although such propulsion systems provide relativelylarge amounts of thrust, rocket propulsion systems are generallypropellant inefficient and have a low specific impulse. As a result,satellites and spacecraft propelled by rocket propulsion systemstypically carry a large proportion of their mass as propellant, leavinga relatively small proportion of the mass available for missionpayloads. Electric propulsion systems provide a viable alternative torocket propulsion systems for long-range or long-duration missions,which require large amounts of propellant. Electric propulsion systemsoperate by using electric energy to expel propellant, typicallyparticles of ionized gas, at high speeds. In this manner, they achieve arelatively high specific impulse and propellant efficiency compared torocket propulsion systems, but produce a relatively small amount ofthrust. These characteristics make electric propulsion systems suitablefor long-range or long-duration missions, where the satellite and/orspacecraft may be accelerated over a long period of time.

SUMMARY

Systems and methods are described herein for mounting a thruster onto avehicle. The system may comprise a thruster mounting structure, thethruster mounting structure comprising a first rotational joint attachedto a vehicle and configured to rotate in a first axis. The thrustermounting structure may further comprise a boom connected to the firstrotational joint, wherein the first rotational joint is configured topivot the boom about the first axis. The thruster mounting structure mayfurther comprise a second rotational joint attached to the boom andconfigured to rotate in the first axis. The thruster mounting structuremay further comprise a third rotational joint attached to the secondrotational joint and configured to rotate in a second axis that isperpendicular to the first axis. The second rotational joint may beconfigured to pivot the third rotational joint about the first axis. Thethruster mounting structure may further comprise a thruster palletattached to the third rotational joint, wherein the third rotationaljoint is configured to pivot the thruster pallet about the second axis,and a thruster that is fixedly attached to the thruster pallet. In someembodiments, the thruster pallet comprises a rectangular face, and thethird rotational joint may be configured to attach to the thrusterpallet along a long edge of the rectangular face.

The vehicle may be any suitable vehicle, including a satellite or otherspacecraft, and may comprise any suitable shape. Although the systemsand methods described herein are discussed in relation to a satellitethat is shaped like a cube or a rectangular prism, other satellite andspacecraft shapes may be contemplated, as will be understood by one ofskill in the art. It will also be understood that the thruster mountingstructure may be mounted on any suitable surface of the vehicle,including a flat surface of a cube/rectangular prism. Other mountingsurfaces may be contemplated as will be understood by those of skill inthe art. Furthermore, although the systems and methods described hereinare described in terms of an electric thruster, it will be understoodthat any suitable thruster may be utilized with the mounting structuredescribed herein.

In some embodiments, the first axis may be a roll axis of the vehicle,and the second axis may be a yaw axis, pitch axis or a combination ofpitch axis and yaw axis of the vehicle. In some embodiments, the firstaxis may be a yaw axis of the vehicle, and the second axis may be a rollaxis, pitch axis or a combination of roll axis and pitch axis of thevehicle. In some embodiments, the first rotational joint and the secondrotational joint may be motorized rotational joints. For example, therotational joints may employ motors, servos, or any other suitablemechanism for changing and maintaining a rotational movement. In someembodiments, the rotational joints may receive control inputs to changeand maintain a rotational angle. In some embodiments, the rotationaljoints may be configured to stiffly maintain a rotational angle until acontrol is received to change the rotational angle. In some embodiments,a second thruster may be connected to the thruster pallet. The secondthruster may be substantially identical to the first thruster, or it maybe substantially different. For instance, the second thruster may beconfigured to provide substantially the same thrust as the firstthruster in order to act as a redundant thruster.

Through the combination of rotational joints, the thruster mountingstructure may be able to orient the thruster pallet in a variety ofpositions, including a stowed position, a station keeping position, andan orbit raising position. In the stowed position, the boom may bepositioned substantially parallel and/or flush to the vehicle and thethruster pallet may be connected to the vehicle. In some embodiments,the thruster pallet may be mated to a retaining receptacle which maysecure the thruster pallet while the thruster pallet is not deployed.For example, the thruster pallet may be secured to the vehicle bodyduring launch to minimize space and to minimize vibration and otherforces on the thruster mounting structure. In some embodiments, thethruster pallet may be kept flush to the vehicle in the stowed position.In some embodiments, the thruster may be facing a directionsubstantially perpendicular to the vehicle or vehicle face that thethruster mounting structure is mounted to. For instance, the thrustermay be faced substantially outward or substantially toward the vehicle,in a direction perpendicular to the vehicle face.

In some embodiments, the thruster mounting structure may be arrangedinto a station keeping position. The station keeping position, asdiscussed in further detail below, may encompass a wide variety oforientations intended to position the thrust vector such that an orbitof the satellite/spacecraft may be maintained. In the station keepingposition, the thruster will be released from the vehicle body andmanipulated using the first, second, and third rotational joints. Insome embodiments, the boom will not be parallel to the vehicle in thestation keeping position. In some embodiments, the boom will be keptperpendicular to the vehicle or a face of the vehicle. In someembodiments, the thrusters in the station keeping position may generatea thrust vector that points through a center of gravity of the vehicle.

In some embodiments, the thruster mounting structure may be arrangedinto an orbit raising position. In the orbit raising position, the boommay be positioned substantially perpendicular to the vehicle or a faceof the vehicle. The thruster pallet may be released from any restrainingreceptacle on the vehicle body. In the orbit raising position, thethruster and/or thruster pallet may be pointed in a directionsubstantially parallel to the vehicle. The thruster may be spaced adistance away from the vehicle, for example, by the boom. In thismanner, the thruster may be positioned to generate a thrust vector thatmay be used to raise or transfer an orbit of the vehicle.

In some embodiments, the system may comprise a second thruster mountingstructure. The second thruster mounting structure may be substantiallysimilar to the first thruster mounting structure. In some embodiments,the vehicle may comprise a rectangular prism shape, and the firstthruster mounting structure and the second thruster mounting structuremay be mounted on opposing faces of the rectangular prism. In thismanner, the first thruster mounting structure and the second thrustermounting structure may be controlled independently in order to changethe vehicles motion, such as orbit altitude, orbit inclination,eccentricity, and/or drift. The second thruster mounting structure maycomprise a fourth rotational joint attached to a vehicle, the fourthrotational joint configured to rotate in the first axis. The fourthrotational joint may be configured to rotate in substantially the sameaxis as the axis of the first rotational joint of the first thrustermounting structure. The second thruster mounting structure may furthercomprise a second boom that may be connected to the fourth rotationaljoint, wherein the fourth rotational joint is configured to pivot theboom about the first axis. The second thruster mounting structure maycomprise a fifth rotational joint, which may be attached to the secondboom and configured to rotate in the first axis. The second thrustermounting structure may further comprise a sixth rotational jointattached to the fifth rotational joint, the sixth rotational jointconfigured to rotate in the second axis, and wherein the fifthrotational joint is configured to pivot the sixth rotational joint aboutthe first axis. The second thruster mounting structure may furthercomprise a second thruster pallet attached to the sixth rotationaljoint, wherein the sixth rotational joint is configured to pivot thesecond thruster pallet about the second axis, and a second thruster maybe fixedly attached to the second thruster pallet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a satellite;

FIG. 2 shows an illustrative diagram of a satellite orbit;

FIG. 3 shows an illustrative diagram of an orbit raising maneuver;

FIG. 4 shows an illustrative diagram of a first and a second thrustermounting structure;

FIG. 5 shows an illustrative diagram of a first and a second thrustermounting structure positioned in a station keeping position;

FIG. 6 shows an illustrative diagram of a first and a second thrustermounting structure positioned in an orbit raising position;

FIG. 7 shows an illustrative diagram of a thruster mounting structurepositioned in a stowed position;

FIG. 8 shows an illustrative diagram of a thruster mounting structurepositioned in a station keeping position;

FIG. 9 shows an illustrative diagram of a thruster mounting structurepositioned in an orbit raising position; and

FIGS. 10A-E show illustrative diagrams of a first and a second thrustermounting structure in various positions.

DETAILED DESCRIPTION

To provide an overall understanding of the systems and methods describedherein, certain illustrative embodiments will now be described. However,it will be understood by one of ordinary skill in the art that thesystems and methods described herein can be adapted and modified forother suitable applications and that such other additions andmodifications will not depart from the scope hereof

Electric thrusters and electric thruster mounting schemes are describedin greater detail in the following U.S. patent documents, which arehereby incorporated by reference herein in their entireties: U.S. Pat.No. 6,032,904, filed Feb. 23, 1998; U.S. Pat. No. 7,059,571, filed Feb.21, 2003; U.S. Pat. No. 6,296,207, filed Jan. 27, 1999; U.S. Pat. No.5,349,532, filed Apr. 28, 1992; U.S. Pat. No. 6,565,043, filed Dec. 21,2001; and U.S. Pat. No. 6,637,701 filed Apr. 3, 2002.

FIG. 1 shows an exemplary embodiment of a satellite 100. The satellite100 may comprise satellite body 102, solar panels 104, solar panelmounting system 105, communications antenna 106, and communicationsantenna mounting system 107. The satellite 100 is provided forillustrative purposes only, and it will be understood that the thrustermounting structure described herein may be integrated into any suitablesatellite.

The satellite body 102 may be any suitable shape, including, but notlimited to, a cube or a rectangular prism. The solar panels 104 may beconfigured to generate electric power from incident sunlight and may bemounted on any suitable face(s) of the satellite body 102 through solarpanel mounting system 105. The solar panel mounting system 105 maycomprise actuators configured to rotate and/or angle the solar panels104. For example, the solar panel mounting system 105 may rotate orangle the solar panels 104 to track the sun in order to generate themost electric power for the satellite. The solar panel mounting system105 may also include means for stowing and/or deploying the solar panels104. For example, the solar panels 104 may be designed to fold forstorage and unfold for deployment. The solar panel mounting system 105may comprise actuators and/or latches to maintain the solar panels in astowed position until a control signal is received to deploy the solarpanels 104. The communications antenna 106 may be any suitable equipmentfor communicating data from the satellite. For instance, thecommunications antenna 106 may generate electromagnetic waves directedtoward a ground station on Earth in order to communicate with missioncontrol. The communications antenna 106 may be connected to thesatellite body 102 through communications antenna mounting system 107.As with the solar panel mounting system 106, the communications antennamounting system 107 may comprise actuators and/or latches formaintaining the communications antenna 106 in a stowed state (e.g.,folded against the satellite body 102) until a control signal isreceived to deploy the communications antenna 106.

The satellite 100 may also comprise one or more of the thruster mountingstructures described in further detail below. The thruster mountingstructure(s) may be mounted or integrated on any suitable surface ofsatellite body 102. For example, two thruster mounting structures may bemounted on the same faces as the solar panels 104, one for each face. Inthis manner, the pair of thruster mounting structures may work in tandemto position two or more thrusters to provide thruster vectoring forstation keeping or orbit raising/transfer maneuvers. The thrustermounting structures may comprise any suitable type of propulsion system.For example, in some embodiments, the thruster mounting structures maycomprise electric thrusters. Any suitable type of electric thruster maybe utilized, including, but not limited to, ion thrusters, plasma-basedthrusters, electrostatic thrusters, electrothermal thrusters, andelectromagnetic thrusters. In some embodiments, the satellite 100 mayfurther comprise traditional rocket-based thrusters mounted on anysuitable surface of the spacecraft body 102, such that the satellite 100is propelled by a combination of a chemical-based rocket propulsionsystem and an electric propulsion system. In these embodiments, thechemical-based rocket propulsion system may be mounted to the satellitebody 102 using the thruster mounting structure described herein, or byany other suitable method. In some embodiments, the satellite 100 maycomprise only an electric propulsion system. In such embodiments, thesatellite 100 may comprise electric thrusters mounted to the satellitebody 102 through a thruster mounting structure as described furtherbelow, in addition to electric thrusters which are mounted to thesatellite body 102 through other means. In this manner, the thrustermounting structures may provide redundant or additional propulsioncapacity in addition to a primary propulsion system.

FIG. 2 shows an illustrative diagram of a satellite orbit 200. Thesatellite 204 may be substantially similar to the satellite 100described in relation to FIG. 1 and may orbit around celestial body 202.Celestial body 202 may be any suitable celestial body, including, butnot limited to, the Earth, the moon, the sun, a planet, a star, or anyother celestial body. The satellite 204 may establish an orbit 206around the celestial body 202. The orbit 206 may comprise one or more ofthe following orbital characteristics: an altitude, a semi-major axis,an eccentricity, an inclination, and argument of periapsis, a longitudeof the ascending node, a time of periapsis passage, a radius ofperiapsis, and a radius of apoapsis. As an illustrative example, acommunications satellite may establish a geostationary (GEO) orbit at analtitude of 35,786 km above the Earth's equator in order to maintain afixed position above the Earth's surface. As another illustrativeexample, an earth-mapping satellite may establish a polar orbit with arelatively high inclination (e.g., close to 90 degrees to the equator)so that it passes the equator at a different longitude on each orbit.The orbit 206 may comprise any suitable shape, including a circularorbit, elliptical orbit, or a figure-eight shape.

In order to maintain its orbit, the satellite 204 may perform stationkeeping maneuvers 208 and 210. As used herein, “station keeping” refersto orbital maneuvers that are required to maintain a desired orbit.Station keeping may be necessary for satellite 204 due to a number ofexternal forces that degrade the orbit of satellite 204, such as airdrag, solar radiation pressure, and gravitational forces from theSun/Moon. In some embodiments, such external forces may decrease orincrease the orbit velocity of the satellite 204, causing the altitude(or semi-major axis) of the orbit 206 to decrease or increaseaccordingly. In such embodiments, the satellite 204 may perform stationkeeping maneuver 208 in the direction of the orbit or the direction oftravel of the satellite 204 in order to increase or decrease the orbitvelocity of the satellite 204 and to counteract the external forces. Insome embodiments, the satellite 204 may perform station keeping maneuver208 according to a feedback loop, such that the orbital velocity and/orthe altitude of the satellite 204 is sensed, and in response todetecting the that orbital velocity and/or the altitude of the satellite204 is not the same as the desired orbital velocity or altitude,performing the station keeping maneuver 208. In some embodiments, thefeedback loop may comprise communication with a ground station on thecelestial body 202 or with another orbiting satellite or spacecraft inorder to determine orbital parameters of the satellite 204. The feedbackloop as discussed above is provided for illustrative purposes only, andit will be understood that any suitable control scheme may be utilizedwith station keeping maneuver 208.

In some embodiments, external forces may provide an increase or decreasein the velocity of the satellite 204 in directions other than thedirection of travel of the satellite 204. Furthermore, the externalforces may impart a net torque or rotation on the satellite 204. In suchinstances, station keeping maneuver 210 may be used to correct for suchvelocity or rotation changes. For example, the external forces mayaffect one or more of the following orbital parameters of orbit 206: aneccentricity, an inclination, and argument of periapsis. As discussedabove in relation to station keeping maneuver 208, a feedback loop maybe used to correct for the changes in the orbital parameters. In someembodiments, one or more of the orbital parameters may be sensed, eitherdirectly by the satellite 204 or by a ground station or anothersatellite, and in response to determining that the sensed orbitalparameter(s) is different than a desired orbital parameter(s),performing station keeping maneuver 210. In some embodiments, acombination of station keeping maneuver 208 and 210 may be utilized tocorrect for changes in orbital parameter(s). Although station keepingmaneuvers 208 and 210 are depicted in FIG. 2 as orthogonal, it will beunderstood that station keeping maneuvers 208 and 210 may point in anysuitable direction for correcting for changes to orbital parameter(s).It will be also understood that station keeping maneuvers 208 and 210may be produced by any suitable thruster(s), including chemicalrocket-based thrusters and electrical thrusters, and any number orcombination of thrusters. For instance, some thruster(s) may beconfigured to point through the center of gravity of the satellite 204and designed to impart a net velocity on the satellite 204, while somethruster(s) may be configured to provide a thrust vector that does notpoint through the center of gravity of the satellite 204 and designed toimpart a net rotation on the satellite 204. Some thruster(s) may beconfigured to impart both a net velocity and a net rotation on thesatellite 204. Some thruster(s) may be fixed in position or rotation,while other thruster(s) may be mounted or gimbaled in a fashion thatallows them to move in at least one of six degrees of freedom (threetranslational, three rotational). For example, one or more of thethrusters mounted onto satellite 204 may be mounted using the thrustermounting structure described herein.

FIG. 3 shows an illustrative diagram of an orbit raising maneuver 300.As used herein, “orbit raising” or “orbit transfer” refers to anyorbital maneuver that changes the orbit of the satellite 304 from afirst orbit 303 to a second orbit 306. Although the orbit raisingmaneuver 300 is depicted in FIG. 3 as a Hohmann transfer, it will beunderstood that the orbit raising maneuver 300 may begin at any initialorbit, be it circular or elliptical, and be any suitable orbitalmaneuver that changes at least one of the following orbital parameters:an altitude, a semi-major axis, an eccentricity, an inclination, andargument of periapsis, a longitude of the ascending node, a time ofperiapsis passage, a radius of periapsis, and a radius of apoapsis.

As depicted in FIG. 3, satellite 304 may orbit around celestial body 302in an initial orbit 303. The satellite 304 may be substantially similarto the satellite 100 depicted in FIG. 1. The celestial body 302 may besubstantially similar to celestial body 202 depicted in FIG. 2. Theinitial orbit 303 may have a radius 305, in addition to other orbitalparameters, below that of the final orbit 306. The initial orbit may bean elliptical orbit, in addition to other orbital parameters, with aperigee below the final orbit 306 and an apogee that can be below, at,or above the final orbit 306. The satellite 304 may perform a multitudeof thruster firings 310 of finite duration at discrete points in theorbit, continuously over one or more orbital revolutions, or anycombination thereof in order to impart the desired change in velocityand reach the final orbit 306. The thruster firing vector 310 may be inthe direction of travel of the satellite 304, opposite of the directionof travel of the satellite 304, or any direction in between. Thethruster firing vector 310 may be at any angle within the orbit andrelative to the orbital plane.

FIG. 4 shows an illustrative diagram of a thruster mounting scheme 400satellite body 402 comprising a first and a second thruster mountingstructure 404. The satellite body 402 may be substantially similar tothe satellite body 102 depicted in FIG. 1 and discussed above. The firstthruster mounting structure 404 comprises a thruster pallet 406, a firstazimuth actuator 408, a second azimuth actuator 410, an elevationactuator 412, thrusters 414, and boom 418. The second thruster mountingstructure 419 may comprise substantially the same components as thefirst thruster mounting structure 404. As depicted in FIG. 4, the firstand second thruster mounting structures 404 and 419 may be mounted onopposite faces of the satellite body 402.

The first azimuth actuator 408 may be configured to rotate in a firstdirection 424. In some embodiments, the direction 424 may be a rotationabout the z axis, as depicted in FIG. 4. In some embodiments, the firstazimuth actuator 408 is configured to rotate only in the first direction424. That is, the first azimuth actuator 408 is stiff in rotation to theother two rotational directions. Similarly, the second azimuth actuator410 may be configured to rotate in a second direction 426, and theelevation actuator 412 may be configured to rotate in direction 428. Aswith the first azimuth actuator 408, the second azimuth actuator 410 andthe elevation actuator 412 may be configured, in some embodiments, torotate only in the respective directions and to be rigid in the otherrotational degrees of freedom. In some embodiments, the first azimuthactuator 408, the second azimuth actuator 410, and the elevationactuator 412 may be motorized actuators configured to receive controlsignals and/or setpoints for rotational position, rotational speed,and/or rotational acceleration.

The thruster pallet 406 may be made of any suitable material, such asmetal, carbon fiber, or composite material. The thruster pallet 406 maybe configured into any suitable shape, including a rectangular prism, asdepicted in FIG. 4. The thrusters 414 may be mounted directly onto thethruster pallet 406 using any suitable means, including, but not limitedto, screws, rivets, bolts, welds, adhesives, or any combination thereof.Although two thrusters 414 are depicted in FIG. 4, it will be understoodthat any number of thrusters may be mounted onto thruster pallet 406.Furthermore, the thrusters 414 may be any suitable type of thruster,including electric thrusters and/or chemical rocket thrusters.

The boom 418 may be made of any suitable material, such as metal, carbonfiber, or composite material. The boom 418 may be any suitable shape andlength. For example, the boom 418 may be a hollow member with a squarecross section. The boom 418 may be attached to one or more of the firstazimuth actuator 408, the second azimuth actuator 410, and/or theelevation actuator 412 using any suitable means, including, but notlimited to, screws, rivets, bolts, welds, adhesives, or any combinationthereof. For instance, the boom 418 may be attached to first azimuthactuator 408 such that the first azimuth actuator 408 may pivot the boomin direction 424. The second azimuth actuator 410 may be attached to thethruster pallet 406 by any suitable means, including, but not limitedto, screws, rivets, bolts, welds, adhesives, or any combination thereof.The second azimuth actuator 410 may be configured to pivot the thrusterpallet 406 in direction 426. In some embodiments, the direction 424 andthe direction 426 may be the same. The elevation actuator 412 may beconnected to the thruster pallet and/or the second azimuth actuator 410.The elevation actuator 412 may be configured to pivot the thrusterpallet 406 in direction 428.

The first azimuth actuator 408 may be attached directly to the satellitebody 402 using any suitable means, including, but not limited to,screws, rivets, bolts, welds, adhesives, or any combination thereof. Thefirst azimuth actuator 408 may rotate the thruster pallet 406 in thedirection 424 to provide a slew angle 422. The slew angle 422 may allowthe thrusters 414 to produce a thrust vector in a direction tangentialto the direction of travel or orbital direction. This may enable controlof the longitude drift rate and eccentricity vector of the satellite. Insome embodiments, the second azimuth actuator 410 may rotate thethruster pallet 406 to provide a thruster direction 420 that pointsthrough the center of gravity of the satellite. Although the center ofgravity of the satellite is depicted as the center of the squarecross-section, the center of gravity may be located at any point withinthe satellite body 402. In some embodiments, the center of gravity maybe outside of the satellite body 402.

FIG. 5 shows an illustrative diagram of a thruster mounting scheme 500including a first and a second thruster mounting structures 504 and 519positioned in a station keeping position. The first and second thrustermounting structures 504 and 519 may be substantially similar to firstand second thruster mounting structures 404 and 419 described inrelation to FIG. 4. Satellite body 502 may be substantially similar tosatellite body 402 described in relation to FIG. 4. As depicted in FIG.5, the first and the second thruster mounting structures 504 and 519 maybe mounted along one edge of the satellite body 502. In the illustrativeexample depicted in FIG. 5, the first and second thruster mountingstructures 504 and 519 are mounted on the y faces of the satellite body502. In the station keeping position, first and second thruster mountingstructures 504 and 519 may use an elevation actuator, such as elevationactuator 412 depicted in FIG. 4, to pivot the thrusters and produce athruster vector 520 that points through the center of gravity of thesatellite. This may produce cant angle 530, measured as the anglebetween the thrust vector 520 and an x-y plane of the spacecraft body502. The cant angle 530 may allow the thrusters 514 to produce a thrustvector that is normal and/or radial to the direction of travel or theorbital direction of the satellite. This may enable control of the orbitinclination and eccentricity vector. In some embodiments, the cant angle530 may enable simultaneous control of the orbit inclination andeccentricity vector. In some embodiments, the velocity of the satellitemay be controlled simultaneously or separately from the angular momentumof the satellite. For example, through the use of cant angle 530 andeither the first azimuth actuator 424 or the second azimuth actuator426, the thrust vector produced by thrusters 414 may be configured topoint through the center of gravity, thereby producing a velocity changebut no torque, or slightly offset from the center of gravity, therebyproducing a net torque. For station keeping maneuvers, the thrusterassociated with either the first thruster mounting structure 504 or thesecond thruster mounting structure 519, or both, may be fired. Asdiscussed above in relation to FIG. 2, the thruster firings may beperformed in order to maintain a certain orbit or orbit characteristics.Through the use of cant angle 530 and slew angle 422 depicted in FIG. 4,a wide range of control options may be enabled for controlling thesatellite body 502, thereby allowing for mission optimization andreduced propellant consumption. In some embodiments, full stationkeeping operations may be completed by the use of two thrusters and twomaneuvers per day or orbital period. In some embodiments, the first anda second thruster mounting structures 504 and 519 may be configured tocontrol six degrees of freedom (three translational, three rotational)of the satellite body 502. Thus, full orbital and station keepingcontrol may be achieved using only two thrusters.

FIG. 6 shows an illustrative diagram of a thruster mounting scheme 600including a first and a second thruster mounting structure 604 and 619positioned in an orbit raising position. The first and second thrustermounting structures 604 and 619 may be substantially similar to firstand second thruster mounting structures 404 and 419 described inrelation to FIG. 4. Satellite body 602 may be substantially similar tosatellite body 402 described in relation to FIG. 4. As depicted in FIG.6, the first and the second thruster mounting structures 604 and 619 maybe mounted along one edge of the satellite body 602. In the illustrativeexample depicted in FIG. 6, the first and second thruster mountingstructures 604 and 619 are mounted on the y faces of the satellite body602. In the orbit raising position, first and second thruster mountingstructures 604 and 619 may use an elevation actuator, such as elevationactuator 412 depicted in FIG. 4, to pivot the thrusters so that theyproduce a thrust vector 620 substantially in the z direction of thevehicle 602 as depicted in FIG. 6. In some embodiments, the z-directionmay be the direction of travel, opposite the direction of travel, oranywhere in between. The cant angle 630 created between the thrustvector 620 and the x-y plane of satellite body 602 may be substantially90 degrees. In some embodiments, the cant angle may point in otherdirections up to and including the direction through the center ofgravity of the vehicle 520 as shown in FIG. 5. For orbit raisingmaneuvers, either one, or both, of the thrusters associated with thefirst and the second thruster mounting structures 604 and 619 may befired. As discussed above in relation to FIG. 3, the thruster firingsmay be performed in order to change the orbit of the satellite from aninitial orbit to a final orbit, and/or to change certain orbitcharacteristics.

FIG. 7 shows an illustrative diagram of a thruster mounting structure704 positioned in a stowed position. The thruster mounting scheme 700,including the spacecraft body 702, the thruster mounting structure 704,the first azimuth actuator 708, the boom 718, the thruster pallet 706,and the thrusters 714, may be substantially similar to the correspondingcomponents discussed above in relation to FIG. 4. In the stowed positiondepicted in FIG. 7, the boom may be substantially parallel to thesatellite body 702. In some embodiments, the boom 718 may be in contactwith the satellite body 702. In some embodiments, the boom 718 may be aspaced distance apart from satellite body 702. In some embodiments, thethruster pallet 706 may be aligned such that the thrusters 714 aresubstantially parallel to the satellite body 702, with thrust vectorsthat point substantially perpendicular to the satellite body 702. Insome embodiments, the thruster pallet 706 may be attached to thesatellite body 702 using a mounting structure. For instance, themounting structure may include actuators intended to keep the thrusterpallet 706 in place during launch, and to deploy the thruster pallet 706at the appropriate time(s) during the satellite's mission.

FIG. 8 shows an illustrative diagram of a thruster mounting structure804 positioned in a station keeping position. The thruster mountingscheme 800, including the spacecraft body 802, the thruster mountingstructure 804, the first azimuth actuator 808, the boom 818, the secondazimuth actuator 810, the thruster pallet 806, and the thrusters 814,may be substantially similar to the corresponding components discussedabove in relation to FIG. 4. In the station keeping position depicted inFIG. 8, the first azimuth actuator 808 may rotate the boom 818 out fromthe satellite body 802. Although the boom 818 in FIG. 8 is depicted assubstantially perpendicular to satellite body 802, it will be understoodthat the boom 818 may be rotated to other angles in the station keepingposition. In some embodiments, the second azimuth actuator 810, and anelevation actuator, such as elevation actuator 412 depicted in FIG. 4,may be used to rotate the thruster pallet 806 so that the thrust vectoris not perpendicular to the satellite body 802. It will be understoodthat the first azimuth actuator 808, the second azimuth actuator 810,and the elevation actuator may be utilized to rotate the thruster palletinto a variety of positions in order to correct for deviations in one ormore orbital parameters, as discussed above in relation to FIG. 2.

FIG. 9 shows an illustrative diagram of a thruster mounting structure904 positioned in an orbit raising position. The thruster mountingscheme 900, including the spacecraft body 902, the thruster mountingstructure 904, the first azimuth actuator 908, the boom 918, the secondazimuth actuator 910, the elevation actuator 912, the thruster pallet806, and the thrusters 914, may be substantially similar to thecorresponding components discussed above in relation to FIG. 4. In theorbit raising position depicted in FIG. 8, the first azimuth actuator908 may rotate the boom 918 out from the satellite body 902. Althoughthe boom 918 in FIG. 9 is depicted as substantially perpendicular tosatellite body 902, it will be understood that the boom 918 may berotated to other angles in the orbit raising position. In someembodiments, the second azimuth actuator 910 and the elevation actuator912 may be used to rotate the thruster pallet 906 so that the thrustvector is substantially parallel to the satellite body 902. As depictedin FIG. 9, the boom 918 may position the thruster pallet 906 and thethrusters 914 a spaced distance from the satellite body 902. In someembodiments, the thrusters 914 produce a combined thrust vector that issubstantially in line with the z-direction of the vehicle In someembodiments, the individual thruster may be rotated such that theindividual thrust vector points anywhere between the z-direction and thedirection through the center of gravity of the vehicle. As discussedabove in relation to FIG. 3, the thrust in this orientation may be usedto change the orbit of the satellite from an initial orbit to a finalorbit.

FIGS. 10A-E show illustrative diagrams 1000 of a first and a secondthruster mounting structures 1004 in various positions. The spacecraftbody 1002, the thruster mounting structure 1004, the first azimuthactuator 1008, the boom 1018, the second azimuth actuator 1010, thethruster pallet 1006, and the thrusters 1014, may be substantiallysimilar to the corresponding components discussed above in relation toFIG. 4. FIG. 10A depicts the first and second thruster mountingstructures 1004 in a stowed position. As discussed above in relation toFIG. 7, in the stowed position, the boom 1018 may be substantiallyparallel and/or flush with the satellite body 1002. The thruster pallet1006 may be rotated to be parallel along its longest edge and such thatthe thrusters point outwards from the satellite body 1002. As discussedin relation to FIG. 7, the thruster pallet 1006 may be secured to thesatellite body 1002 using a mounting scheme, wherein the mounting schemeis configured to release or deploy the thruster pallet 1006 at anappropriate time(s) during the satellite's mission. In this manner, thestowed position may minimize the storage space required and minimize anyadverse forces imparted on the thruster pallet 1006, for example, duringlaunch.

FIG. 10B depicts the first and second thruster mounting structures 1004in an orbit raising position. As discussed above in relation to FIGS. 6and 9, in the orbit raising position, the thrusters 1014 may be rotatedsuch that the combined thruster vector points substantially in thez-direction. In some embodiments, the thrusters may be rotated such thatthe individual thrust vector points anywhere between the z-direction andthe direction through the center of gravity of the vehicle. As discussedabove in relation to FIG. 3, the thrust in the z-direction may increasethe velocity of the satellite and result in a change of orbit. Asdepicted in FIG. 10B, the boom 1018 may not be perpendicular to the x-zfact of the satellite body 1002. In some embodiments, for orbit raisingmaneuvers, both of the thrusters associated with the first and thesecond thruster mounting structure may be fired in order to reduce anyunwanted rotation on the satellite body 1002.

FIG. 10C depicts the first and second thruster mounting structures 1004in a station keeping position. As discussed above in relation to FIGS. 5and 8, in the station keeping position, the thrusters 1014 may berotated into a variety of positions to correct for deviations in certainorbit parameters. In the position depicted in FIG. 10C, the first andsecond thruster mounting structures 1004 may correct for deviations inboth inclination and eccentricity. For instance, the orientation of thethrusters 1014 may produce forces in both the z direction and the ydirection, which may compensate for external forces in those directions.As depicted in FIG. 10C, the boom 1018 may not be perpendicular to thex-z fact of the satellite body 1002. In some embodiments, for stationkeeping maneuvers, one or both the of the thrusters associated with thefirst and the second thruster mounting structure may be fired as neededto correct for orbital deviations.

FIGS. 10D and E depict the first and second thruster mounting structures1004 in other station keeping positions. As discussed above in relationto FIGS. 5 and 8, in the station keeping position, the thrusters 1014may be rotated into a variety of positions to correct for deviations incertain orbit parameters. In the positions depicted in FIGS. 10D and E,the first and second thruster mounting structures 1004 may correct fordeviations in inclination, eccentricity, and drift. For instance, theorientation of the thrusters 1014 may produce forces in all of the x, y,and z directions, which may compensate for external forces in thosedirections. The angle of the thrust vector may be controlled using thefirst azimuth actuator 1008, the second azimuth actuator 1010, and anelevation actuator such as elevation actuator 412 depicted in FIG. 4. Asdepicted in FIGS. 10D and E, the boom 1018 may not be perpendicular tothe x-z fact of the satellite body 1002. In some embodiments, forstation keeping maneuvers, one or both the of the thrusters associatedwith the first and the second thruster mounting structure may be firedas needed to correct for orbital deviations.

In some embodiments, depending on the location of the center of gravityof the satellite, the orientations depicted in FIGS. 10B, C, D and E mayalso impart a net torque and/or rotation on the satellite body 1002.

It will be apparent to those skilled in the art that the embodimentsdescribed herein are provided by way of example only. It should beunderstood that numerous variations, alternatives, changes, andsubstitutions may be employed by those skilled in the art in practicingthe invention. Accordingly, it will be understood that the invention isnot to be limited to the embodiments disclosed herein, but is to beunderstood from the following claims, which are to be interpreted asbroadly as allowed under the law.

1. A thruster system for mounting onto a space structure, the systemcomprising: a first rotational joint, the first rotational jointconfigured to rotate in an axis; a support connected to the firstrotational joint, wherein the first rotational joint is configured topivot the support in rotation; a second rotational joint, the secondrotational joint attached to the support and configured to rotate in afirst axis; a third rotational joint attached to the second rotationaljoint, the third rotational joint configured to rotate in a second axisthat is perpendicular to the first axis, wherein the second rotationaljoint is configured to pivot the third rotational joint in rotation; athruster pallet attached to the third rotational joint, wherein thethird rotational joint is configured to pivot the thruster pallet inrotation; and a thruster fixedly attached to the thruster pallet.
 2. Thesystem of claim 1, wherein the thruster pallet comprises a rectangularface, and wherein the third rotational joint is configured to attach tothe thruster pallet along a long edge of the rectangular face. 3-10.(canceled)
 11. The system of claim 1, wherein the first axis is one of:a roll axis of the vehicle and a yaw axis of the vehicle.
 12. The systemof claim 11, wherein the second axis is perpendicular to the first axisanywhere within the pitch-yaw plane or pitch-roll plane of the vehicle.13. The system of claim 1, wherein at least two of the first rotationaljoint, the second rotational joint, and the third rotational joint aremotorized rotational joints.
 14. The system of claim 1, wherein thethruster is an electric thruster.
 15. The system of claim 1, wherein asecond thruster is attached to the thruster pallet.
 16. The system ofclaim 16, wherein the second thruster is substantially identical to thethruster. 17-20. (canceled)
 21. A thruster system comprising: a mountingstructure for attaching to a space vehicle, the mounting structureincluding: a first rotational joint, the first rotational jointconfigured to rotate in an axis; a boom connected to the firstrotational joint, wherein the first rotational joint is configured topivot the boom in rotation; a second rotational joint, the secondrotational joint attached to the support and configured to rotate in afirst axis; and a third rotational joint attached to the secondrotational joint, the third rotational joint configured to rotate in asecond axis perpendicular to the first axis, wherein the secondrotational joint is configured to pivot the third rotational joint inrotation; and a thruster structure configured for attachment to themounting structure via the third rotational joint, the thrusterstructure including: a thruster pallet, wherein the third rotationaljoint is configured to pivot the thruster pallet in rotation; and athruster fixedly attached to the thruster pallet.
 22. A space structurecomprising: a first rotational joint attached to the space structure,the first rotational joint configured to rotate in an axis; a supportconnected to the first rotational joint, wherein the first rotationaljoint is configured to pivot the support in rotation; a secondrotational joint, the second rotational joint attached to the supportand configured to rotate in a first axis; a third rotational jointattached to the second rotational joint, the third rotational jointconfigured to rotate in a second axis that is perpendicular to the firstaxis, wherein the second rotational joint is configured to pivot thethird rotational joint in rotation; a thruster pallet attached to thethird rotational joint, wherein the third rotational joint is configuredto pivot the thruster pallet in rotation; and a thruster fixedlyattached to the thruster pallet.
 23. The space structure of claim 22,wherein the first rotational joint is attached to the space structurevia a thruster mounting structure.
 24. The space structure of claim 22,wherein the thruster pallet is configurable into a stowed position wherethe support is positioned substantially flush with the space structureand the thruster pallet is directly connected to the space structure.25. The space structure of claim 22, wherein the thruster pallet isconfigurable into a station keeping position where the support is notflush with the vehicle and the thruster pallet is not directly connectedto the space structure.
 26. The space structure of claim 22, wherein thethruster is configurable so that a thrust vector generated by thethruster points through a center of gravity of the space structure. 27.The space structure of claim 22, wherein the thruster pallet isconfigurable into an orbit raising position where the support ispositioned substantially perpendicular to the space structure.
 28. Thespace structure of claim 22, further comprising: a fourth rotationaljoint attached to the space structure, the fourth rotational jointconfigured to rotate in an axis; a second support connected to thefourth rotational joint, wherein the fourth rotational joint isconfigured to pivot the second support in rotation; a fifth rotationaljoint, the fifth rotational joint attached to the second support andconfigured to rotate in the first axis; a sixth rotational jointattached to the fifth rotational joint, the sixth rotational jointconfigured to rotate in the second axis that is perpendicular to thefirst axis, wherein the fifth rotational joint is configured to pivotthe sixth rotational joint in rotation; a second thruster palletattached to the sixth rotational joint, wherein the sixth rotationaljoint is configured to pivot the second thruster pallet in rotation; anda thruster fixedly attached to the second thruster pallet.
 29. The spacestructure of claim 28, wherein the thruster pallet and the secondthruster pallet are configured to control six degrees of freedom of thespace structure.